Most swept-wavelength lasers calibrate one or more control parameters to the output wavelength, with limited control over the presence of additional longitudinal modes of the laser cavity (e.g., side modes). Side modes can reduce the effectiveness of the laser for interferometric measurements by limiting the dynamic range of the fringes. In a telecommunications testing or sensing application, excessive side modes may limit the minimum detectable power through a component, or create a blurring of the edges of a device being characterized. The metric for measuring the amplitudes of side modes is the side mode suppression ratio (SMSR), which is the ratio of the largest side mode relative to the primary mode of the laser.
In monolithic semiconductor lasers comprising multiple sections, the laser control parameters provide more control over the wavelength and SMSR. Examples of these lasers are vernier-tuneable distributed Bragg Reflector lasers (VTDBRs), which include back mirror, gain, phase, and front mirror sections. The laser may also have a section outside the laser cavity for amplification, sometimes called a Semiconductor Optical Amplifier (SOA).